Terminally functional polymers of isobutylene are of great interest in that they may serve as precursors to the production of block copolymers having blocks of polyisobutylene and blocks of a variety of polymers of anionically polymerizable monomers. Block copolymers of polyisobutylene and polybutadiene are of interest because they represent a way in which incompatible butyl rubber and polybutadiene may be compatibilized and advantage thereby taken of butyl rubber's unique properties in formulating compounds for tire tread applications. Block copolymers of polyisobutylene with polystyrene, poly-alpha-methylstyrene or styrene-indene copolymers are of interest because they exhibit both elastomeric as well as thermoplastic characteristics, behaving like vulcanized rubbers at room temperature, and like thermoplastic polymers at higher temperatures. Thus, such materials can be melt extruded like plastics while retaining their beneficial rubbery features upon cooling. Block copolymers of polyisobutylene and polymers of acrylate monomers are of interest because they provide a means of toughening or improving the impact resistance of acrylate thermoplastics. Thus, it would be advantageous to develop a polyisobutylene with a terminal functionality that is appropriate for the production of block copolymers of polyisobutylene with polymers of anionically polymerizable monomers. Such a terminal functionality is an allylic halogen which will readily undergo a nucleophilic substitution reaction with an anion and in particular, a living polymer anion.